The invention pertains to an aqueous 1-component composition which forms a resilient silicone network on drying.
All water-based silicone coating systems based on crosslinking silicones have required an additional catalyst component which, for example, is added only shortly before actual use, in order to prevent premature gellation. A typical example is the platinum-catalyzed vulcanization of silicones containing vinyl groups with silicones carrying Sixe2x80x94H groups, for example in paper coating or fabric coating. The following aqueous composition is known for coating as an emulsion:
1) An oil-in-water emulsion of siloxane oils carrying vinyl groups which are stabilized with anionic or nonionic surfactants;
2) An oil-in-water emulsion of siloxane oils carrying Sixe2x80x94H groups which are stabilized with anionic or nonionic surfactants;
3) Optionally a filler;
4) A catalyst component (platinum compound); and
5) Optionally an inhibitor.
A further type of crosslinkable emulsion is based on crosslinking silicone oils having xcex1,xcfx89-alkoxy or hydroxyl functions, which is catalyzed with the aid of metal salts, e.g. tin compounds, which optionally may also contain borates. Such systems have the following composition:
1) An oil-in-water emulsion of xcex1,xcfx89-dihydroxypolyorganosiloxane and/or xcex1,xcfx89-dialkoxyorganosiloxane, stabilized with an anionic or nonionic surfactant;
2) A crosslinking agent, such as colloidal silica gel, sodium silicate (=catalyst), siliconates, or microemulsions of silsesquioxanes or silicone resins, polysilicates, polyalkoxysilanes;
3) An inorganic or organic filler; and
4) A catalyst for curing (e.g. salts of the metals tin, lead, calcium, barium, zirconium or iron).
The two water-based coating systems described above also have further disadvantages in addition to the aforementioned catalyst problem:
A) the individual components or at least the catalyst component must be stored separately and can be mixed in only shortly before use, i.e. complicated process engineering during application;
B) the emulsions have only very limited shelf-life, shear stability and thermal stability;
C) in the case of high solids contents, the viscosity increases greatly;
D) the compositions exhibit high shrinkage on drying; and
E) the compositions demonstrate poor adhesion to the substrate.
A further type of system crosslinkable in situ comprises, for example, silicone oils which carry xcex1,xcfx89-dialkoxy-terminated amino groups which readily crosslink on application (e.g. to textiles). The disadvantage of this type of coating is its low crosslinking density and problems associated therewith, such as poor mechanical properties, poor permanence on the substrate, a large amount of extractables, xe2x80x9cexudationxe2x80x9d of silicone oil, etc.
An object of the present invention was to provide an aqueous 1-component system which has a long shelf-life and forms a resilient silicone network on drying, without the addition of a catalyst.
The invention pertains to aqueous 1-component compositions which form resilient silicone networks on drying and are obtained by reaction, at a temperature of at least 40xc2x0 C., of
I) a surfactant-stabilized dispersion of at least one highly crosslinked silicone compound which carries reactive groups, selected from silanol, hydrocarbon-oxy and silanolate groups with
II) a surfactant-stabilized emulsion of at least one optionally precrosslinked silicone oil which carries reactive groups, selected from silanol, hydrocarbon-oxy and silanolate groups.
This composition cures on drying without the addition of a catalyst. The composition is distinguished by its long shelf-life, even at elevated temperature, and its high shear stability. At the same time, low viscosities at high solids content and filler content can be achieved with this composition.
Silicone dispersion (I), which may also be referred to as polyorganosilicic acid sol, preferably contains highly crosslinked silicone compound (Ia) composed of units of the general formulae (Ia-1) to (Ia-4):
in which
R may be identical or different and is a hydrogen atom or an Sixe2x80x94C-bonded C1- to C30-hydrocarbon radical which optionally may also be substituted by halogen atoms or may carry one or more functional groups,
R1 may be identical or different and may be a hydrogen atom, an alkali metal or alkaline earth metal atom, or a monovalent C1- to C16-hydrocarbon radical which optionally may also carry halogen atoms, the hydrocarbon chain of which may be interrupted by hetero atoms such as oxygen,
a is 0 or 1,
b is 0, 1, 2 or 3 and
c is 0 or 1.
Examples of functional groups which may be present in R are double bonds such as the vinyl group, the acrylate group, etc.; or amino groups such as the aminopropyl or aminopropylaminoethyl group or a cyclohexylamine group; a mercapto group such as the mercaptopropyl group; epoxy groups; acid anhydride groups; acid groups; etc. Preferred radicals R in each case are the C1- to C6-alkyl radicals and the phenyl radical, in particular the unsubstituted radicals of these types, and the methyl radical.
Silicone compound (Ia) preferably contains, in each case independently of one another,
60 to 100 mol % of units of the general formula Ia-1,
60 to 100 mol % of units of the general formula Ia-2,
0 to 40 mol % of units of the general formula Ia-3,
0 to 20 mol % of units of the general formula Ia-4.
Silicone dispersion (I) may contain silanes of the general formula (Ib)
R(4xe2x88x92d)Si(OR1)dxe2x80x83xe2x80x83(Ib)
in which
R and R1 have the above meaning and
d may be 1, 2, 3 or four.
100 parts of silicone dispersion (I) preferably contain 1 to 50 parts, in particular 5 to 30 parts, of silicone compound (Ia) and 0.5 to 20 parts, in particular 1 to 10 parts, of surfactant and may also contain 0 to 30 parts, in particular 5 to 20 parts, of an alcohol and 0 to 5 parts, in particular 0 to 2 parts, of the silane of the general formula (Ib). The remaining amount to 100 parts in each case comprises water. xe2x80x9cPartsxe2x80x9d as used herein means parts on a mass basis.
Silicone oil emulsion (II) contains silicone oils of the general formula II
(R1O)(3xe2x88x92e)ReSiOxe2x80x94(R2SiO)xxe2x80x94(RSiO3/2)yxe2x80x94(SiO4/2)zxe2x80x94Oxe2x80x94SiRe(R1O)(3xe2x88x92e)
in which
R and R1 have the above meanings and
e is 0, 1 or 2,
x is 2 to 1,000,000,
y is 0 to 100,000, in particular 0 to 100, and
z is 0 to 100,000, in particular 0 to 100, and
y+z: x is not more than 1:10, in particular not more than 1:40.
100 parts of the silicone oil emulsion (II) preferably contain 1 to 60 parts, in particular 20 to 40 parts, of silicone oils (IIa) and 0.5 to 40 parts, in particular 5 to 15 parts, of surfactant, and may also contain 0 to 20 parts, in particular 0 to 10 parts, of an alcohol and 0 to 5 parts, in particular 0 to 2 parts, of the silane of the general formula (Ib). The remaining amount to 100 parts in each case, comprises water. Silicone oil emulsion (II) is preferably of the oil-in-water type.
The pH of the silicone dispersion (I) and of the silicone oil emulsion (II) may vary in each case from 0 to 14.
In addition, the composition may also contain 0 to 100 parts of acidic, neutral, basic, inorganic or organic additives, such as fillers, water-soluble or water-dispersible oligomers or polymers. The additives may originate from the silicone dispersion (I) and/or from the silicone oil emulsion (II) or may be added to the composition. The solids content of the composition may vary preferably from 5% by weight to 90% by weight, with 20 to 70% by weight solids being particularly preferred, in particular 25 to 40% by weight solids.
Preferred examples of inorganic fillers are precipitated silica, pyrogenic silica, titanium dioxide, basic or acidic aluminas, etc. Organic fillers are, for example, aqueous latices, such as SBR latex, etc.
Preferred examples of water-soluble or water-dispersible oligomers or polymers are nonionic compounds, such as polyethylene glycols and polyethylenepolypropylene copolymers in a molar mass range from 200 g/mol to 20,000 g/mol, or polyelectrolytes, such as polyacrylic acids, etc.
Preferred examples of alcohols used are primary C1- to C6-alcohols, such as methanol, ethanol, butanol, or secondary C3- to C8-alcohols, such as isopropanol, 2-butanol, etc., or tertiary C4- to C8-alcohols, such as tert-butanol, etc.
The surfactants used may be ionic or nonionic. Mixtures of surfactants may also be used. Particularly suitable surfactants are:
Alkylsulfates, for example having a chain length of 8-18 C atoms, aryl and alkyl ether sulfates having 8-18 C atoms in the hydrophobic radical and 1-40 ethylene oxide (EO) or propylene oxide (PO) units;
sulfonates, e.g. alkanesulfonates having 8-18 C atoms, alkylarylsulfonates having 8-18 C atoms, esters and monoesters of sulfosuccinic acid with monohydric alcohols or alkylphenols having 4-15 C atoms; these alcohols or alkylphenols may optionally also be ethoxylated with 1-40 EO units;
alkali metal and ammonium salts of carboxylic acids having 8-20 C atoms in the alkyl, aryl, alkaryl or arylalkyl radical;
partial esters of phosphoric acid and their alkali metal and ammonium salts, e.g. alkyl and alkaryl phosphates having 8-20 C atoms in the organic radical, alkyl ether or alkaryl ether phosphates having 8-20 C atoms in the alkyl or alkaryl radical and 1-40 EO units;
alkyl polyglycol ethers having 2-40 EO units and alkyl radicals of 4-20 C atoms;
alkylaryl polyglycol ethers having 2-40 EO units and 8-20 C atoms in the alkyl and aryl radicals;
ethylene oxide/propylene oxide (EO/PO) block copolymers having 8-40 EO and PO units;
fatty acid polyglycol esters having 6-24 C atoms and 2-40 EO units;
alkylpolyglycosides, natural substances and their derivatives, such as lecithin, lanolin, saponins, cellulose; cellulose alkyl ethers and carboxyalkyl-celluloses whose alkyl groups each have up to 4 carbon atoms;
linear organo(poly)siloxanes containing polar groups and having alkoxy groups having up to 24 C atoms and/or up to 40 EO and/or PO groups;
salts of primary, secondary and tertiary fatty amines having 8-24 C atoms with acetic acid, sulfuric acid, hydrochloric acid and phosphoric acids;
quaternary ammonium salts, such as halides, sulfates, phosphates, acetates or hydroxides, whose alkyl groups, independently of one another, have 1-24 C atoms; optionally, some of the alkyl or alkaryl or aralkyl groups of the quaternary ammonium compounds may also be ethoxylated (1-40 EO units); and
alkylpyridinium, alkylimidazolinium and alkyloxazolinium salts whose alkyl chain has up to 18 C atoms, in the form of their halides, sulfates, phosphates or acetates.
Aliphatically substituted benzenesulfonic acids and their salts and optionally partially ethoxylated quaternary ammonium halides and hydroxides are preferred. Dodecylbenzenesulfonic acid and benzyldimethyl{2-[2-(p-1,1,3,3-tetra-methylbutylphenoxy)ethoxy]ethyl}ammonium chloride (benzethonium chloride) are particularly preferred.
The formulation according to the invention may be composed of the components (I) and (II) as follows:
0.5 to 90 parts of the silicone dispersion (I) and
99.5 to 10 parts of the silicone oil emulsion (II).
The invention also relates to a process for the preparation of the aqueous 1-component composition which forms a resilient silicone network on drying, in which
(I) a surfactant-stabilized dispersion of a highly crosslinked silicone compound which carries reactive groups which are selected from silanol, hydrocarbon-oxy and silanolate groups is reacted, at at least 40xc2x0 C., with
II) a surfactant-stabilized emulsion of optionally precrosslinked silicone oil which carries reactive groups which are selected from silanol, hydrocarbon-oxy and silanolate groups.
In the reaction of silicone dispersion (I) with silicone oil emulsion (II) to give the aqueous 1-component composition, preferably 0.5 to 90 parts, in particular 1 to 20 parts, of the silicone dispersion (I) and 99.5 to 10 parts, in particular 99 to 60 parts, of the silicone oil emulsion II are used.
The reaction can be carried out without a catalyst or can be catalyzed by acid or base. The catalysts used for the reaction can remain in the composition or can be removed. For the preparation of the composition, all components of the composition are preferably combined in the ratios described above and reacted optionally with the addition of a homogeneous or heterogeneous catalyst. When heterogeneous catalysts are used, the possible filler addition is not effected until after the reaction.
Suitable catalysts are heterogeneous acidic or basic systems, such as acidic or basic aluminas, etc. The heterogeneous catalysts can be filtered off after the reaction.
Preferred reaction temperatures are 45xc2x0 C. to 100xc2x0 C., in particular 45xc2x0 C. to 80xc2x0 C. and most preferably 50 to 70xc2x0 C.
The solids content of the composition may be adjusted by removing water or alcohol. A suitable method for this purpose is, for example, distillation at atmospheric pressure or reduced pressure.
The invention also relates to the use of this composition for coating various substrates, such as paper, films, textiles and woven fabrics, glass, metal, etc., and the use as silicone sealing compounds.
In the examples described below, all stated parts and percentages are based on weight, unless stated otherwise. Furthermore, all viscosity data relate to a temperature of 25xc2x0 C. Unless stated otherwise, the examples below were carried out at a pressure of the ambient atmosphere, i.e. about 1000 hPa, and at room temperature, i.e. at about 20xc2x0 C., or at a temperature which is established on combining the reactants without additional heating or cooling.
The following abbreviations are used:
CS: pyrogenically prepared colloidal silica